(1) Field of the Invention
The invention relates to gas turbine engine components, and more particularly to an aerodynamic profile for an airfoil and a blade comprising an airfoil with such a profile.
(2) Description of the Related Art
The efficiency of a gas turbine engine is directly related to the individual efficiencies of the major sections included therein. The turbine section contains bladed rotors, which extract power from hot combustion gases and transfer the power to a compressor section via common shafting. The efficiency of an airfoil portion of the blades determines the quantity of power extracted and conversely, the quantity of power that is wasted due to inefficiencies. Since the cost of fuel is a very important business consideration for gas turbine operators, any improvement to the aerodynamic efficiency of the airfoils is extremely beneficial.
During operation, turbine blades are exposed to combustion gases with temperatures that may exceed their melting temperature and must be thermally protected to extend their durability and useable life. Typically, blades are cooled by internal air passages and insulated externally by thermal barrier coatings. Various examples of internal air passages may be seen in the references incorporated herein. Internal passages are designed to provide adequate cooling for the airfoil, while not limiting the structural strength of the entire blade. Thermal barrier coatings of the type described in U.S. Pat. No. 5,262,245 to Ulion, et al., are applied to the airfoils of the blade with a thickness that varies based on the location on the airfoil. Airfoil locations that are exposed to the hottest combustion gas temperatures require a thicker coating.
The addition of thicker coatings to an airfoil may negatively affect the aerodynamic efficiency of an airfoil and specifically, an airfoil's ability to direct an adequate volume of combustion gases rearward. By increasing an airfoil's coating thickness, the area between adjacent airfoils is decreased; therefore, reducing the aerodynamic efficiency and ability to discharge an adequate volume of combustion gases. What is needed is an airfoil profile that will accept an increased coating thickness while maintaining an adequate area between adjacent airfoils.